U.S. patent application number 15/850521 was filed with the patent office on 2019-06-27 for sensor fault detection using paired sample correlation.
The applicant listed for this patent is Robert Bosch Battery Systems, LLC, Robert Bosch GmbH. Invention is credited to Carlton Brown, Blake Joseph Riley.
Application Number | 20190195952 15/850521 |
Document ID | / |
Family ID | 64900854 |
Filed Date | 2019-06-27 |
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United States Patent
Application |
20190195952 |
Kind Code |
A1 |
Riley; Blake Joseph ; et
al. |
June 27, 2019 |
SENSOR FAULT DETECTION USING PAIRED SAMPLE CORRELATION
Abstract
A battery system and paired sample correlation method for
current sensor fault detection in the battery system is disclosed.
The method comprises receiving a sequence of battery voltage
samples from a voltage sensor configured to measure a battery
voltage of a battery and a sequence of battery current samples from
a current sensor configured to measure a battery current of the
battery; determining a change in the battery voltage samples over a
predetermined number of samples and a change in the battery current
samples over the predetermined number of samples; checking whether
a ratio of the change in the battery voltage samples and the change
in the battery current samples is within an expected range for one
of (i) a resistance of the battery and (ii) a conductance of the
battery; and detecting a fault in the current sensor based on
whether the ratio is within the expected range.
Inventors: |
Riley; Blake Joseph;
(Chesterfield, MI) ; Brown; Carlton; (Royal Oak,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch Battery Systems, LLC
Robert Bosch GmbH |
Orion
Stuttgart |
MI |
US
DE |
|
|
Family ID: |
64900854 |
Appl. No.: |
15/850521 |
Filed: |
December 21, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 31/382 20190101;
G01R 31/374 20190101; G01R 31/2829 20130101; G01R 31/08 20130101;
G01R 31/389 20190101; G01R 35/00 20130101; G01R 31/3842
20190101 |
International
Class: |
G01R 31/36 20060101
G01R031/36; G01R 31/08 20060101 G01R031/08 |
Claims
1. A method of current sensor fault detection comprising: receiving
a sequence of battery voltage samples from a voltage sensor
configured to measure a battery voltage of a battery and a sequence
of battery current samples from a current sensor configured to
measure a battery current of the battery; determining a change in
the battery voltage samples over a predetermined number of samples
and a change in the battery current samples over the predetermined
number of samples; checking whether a ratio of the change in the
battery voltage samples and the change in the battery current
samples is within an expected range for one of (i) a resistance of
the battery and (ii) a conductance of the battery; and detecting a
fault in the current sensor based on whether the ratio is within
the expected range.
2. The method according to claim 1, the determining of the change
in the battery voltage samples and the change in the battery
current samples further comprising: determining the change in the
battery voltage samples as a difference between a value of the
battery voltage samples at a first time step and a value of the
battery voltage samples at a second time step, the second time step
being a first predetermined number of time steps after the first
time step; and determining the change in the battery current
samples as a difference between a value of the battery current
samples at a third time step and a value of the battery current
samples at a fourth time step, the fourth time step being the first
predetermined number of time steps after the third time step, the
third time step being a second predetermined number of time steps
before or after the first time step
3. The method according to claim 1 further comprising: receiving a
battery temperature measurement from a temperature sensor
configured to measure a temperature of the battery; and determining
the expected range based on the battery temperature
measurement.
4. The method according to claim 1, the detecting further
comprising: detecting the fault based on the ratio being outside
the expected range.
5. The method according to claim 1 further comprising: repeating
the steps of determining and checking for successive time steps of
the battery voltage samples and battery current samples; storing,
for each repetition of the check, whether the ratio is outside the
expected range; determining, after a predetermined number of
repetitions of the check, a number of times of the predetermined
number of repetitions that the ratio was outside the expected
range; and detecting the fault in response to the number of times
exceeding a predetermined threshold.
6. The method according to claim 5 further comprising: adjusting at
least one of the expected range and the predetermined threshold
based on at least one of (i) cell aging of the battery, (ii) a
state of charge of the battery, (iii) a polarity of the battery
current, and (iv) a phase difference between the battery current
and battery voltage.
7. The method according to claim 1, the checking further
comprising: only performing the check if at least one of (i) a
battery temperature of the battery exceeds a minimum temperature
threshold, (ii) the change in the battery voltage samples exceeds a
minimum voltage change threshold, and (iii) a current value of the
battery current samples exceeds a minimum current threshold.
8. The method according to claim 7 further comprising: adjusting at
least one of the minimum temperature threshold, the minimum voltage
change threshold, and the minimum current threshold based on at
least one of (i) cell aging of the battery, (ii) a state of charge
of the battery, (iii) a polarity of the battery current, and (iv) a
phase difference between the battery current and battery
voltage.
9. The method according to claim 1 further comprising: operating,
in response to detecting the fault, an output device to generate
one of (i) an audible alert and (ii) a visual alert.
10. The method according to claim 1 further comprising: operating,
in response to detecting the fault, at least one switch to
disconnect the battery from at least one load.
11. A battery system comprising: a battery operably connected to
provide power to at least one load; a voltage sensor configured to
measure a battery voltage of the battery; a current sensor
configured to measure a battery current of the battery; and a
controller operably connected to the voltage sensor and the current
sensor, the controller being configured to: receive a sequence of
battery voltage samples from the voltage sensor and a sequence of
battery current samples from the current sensor; determine a change
in the battery voltage samples over a predetermined number of
samples and a change in the battery current samples over the
predetermined number of samples; check whether a ratio of the
change in the battery voltage samples and the change in the battery
current samples is within an expected range for one of (i) a
resistance of the battery and (ii) a conductance of the battery;
and detect the fault in the current sensor based on whether the
ratio is within the expected range.
12. The battery system according to claim 11, the controller being
further configured to: determine the change in the battery voltage
samples as a difference between a value of the battery voltage
samples at a first time step and a value of the battery voltage
samples at a second time step, the second time step being a first
predetermined number of time steps after the first time step; and
determine the change in the battery current samples as a difference
between a value of the battery current samples at a third time step
and a value of the battery current samples at a fourth time step,
the fourth time step being the first predetermined number of time
steps after the third time step, the third time step being a second
predetermined number of time steps after the first time step
13. The battery system according to claim 11 further comprising: a
temperature sensor configured to measure a temperature of the
battery, wherein the controller is further configured to: receive a
battery temperature measurement from the temperature sensor; and
determine the expected range based on the battery temperature
measurement.
14. The battery system according to claim 11, the controller being
further configured to: detect the fault in response to the ratio
being outside the expected range.
15. The battery system according to claim 11, the controller being
further configured to: repeat the determination and the check for
successive time steps of the battery voltage samples and battery
current samples; store, for each repetition of the check, whether
the ratio is outside the expected range; determine, after a
predetermined number of repetitions of the check, a number of times
of the predetermined number of repetitions that the ratio was
outside the expected range; and detect the fault in response to the
number of times exceeding a predetermined threshold.
16. The battery system according to claim 15, the controller being
further configured to: adjust at least one of the expected range
and the predetermined threshold based on at least one of (i) cell
aging of the battery, (ii) a state of charge of the battery, (iii)
a polarity of the battery current, and (iv) a phase difference
between the battery current and battery voltage.
17. The battery system according to claim 11, the controller being
further configured to: only perform the check if at least one of
(i) a battery temperature of the battery exceeds a minimum
temperature threshold, (ii) the change in the battery voltage
samples exceeds a minimum voltage change threshold, and (iii) a
current value of the battery current samples exceeds a minimum
current threshold.
18. The battery system according to claim 17, the controller being
further configured to: adjust at least one of the minimum
temperature threshold, the minimum voltage change threshold, and
the minimum current threshold based on at least one of (i) cell
aging of the battery, (ii) a state of charge of the battery, (iii)
a polarity of the battery current, and (iv) a phase difference
between the battery current and battery voltage.
19. The battery system according to claim 11, the controller being
further configured to: operate, in response to detecting the fault,
an output device to generate one of (i) an audible alert and (ii) a
visual alert.
20. The battery system according to claim 11, the controller being
further configured to: operate, in response to detecting the fault,
at least one switch to disconnect the battery from the at least one
load.
Description
FIELD
[0001] The device and method disclosed in this document relates to
battery systems and, more particularly, to sensor fault detection
in battery systems.
BACKGROUND
[0002] Battery systems often include one or more sensors configured
to monitor parameters of the battery, such as current and voltage,
during operation. It many applications, reliable monitoring of
battery parameters is critical to safe and efficient operation of
the battery system. In certain automotive applications, on-board
diagnostics (OBD) regulations require a two-sided rationality check
for detecting current sensor faults. The current state of the art
for detecting faults in a battery system's current sensor generally
requires the inclusion of a second redundant current sensor. The
system compares values of the two different current sensors. If the
sensors' values differ too much, a fault will be suspected by the
system. Accordingly, it would be advantageous to provide a system
and method for detecting current sensor faults in a battery system
having only one current sensor.
SUMMARY
[0003] A method of current sensor fault detection is disclosed. The
method comprises: receiving a sequence of battery voltage samples
from a voltage sensor configured to measure a battery voltage of a
battery and a sequence of battery current samples from a current
sensor configured to measure a battery current of the battery;
determining a change in the battery voltage samples over a
predetermined number of samples and a change in the battery current
samples over the predetermined number of samples; checking whether
a ratio of the change in the battery voltage samples and the change
in the battery current samples is within an expected range for one
of (i) a resistance of the battery and (ii) a conductance of the
battery; and detecting a fault in the current sensor based on
whether the ratio is within the expected range.
[0004] A battery system is disclosed. The battery system comprises
includes: a battery operably connected to provide power to at least
one load; a voltage sensor configured to measure a battery voltage
of the battery; a current sensor configured to measure a battery
current of the battery; and a controller operably connected to the
voltage sensor and the current sensor. The controller is configured
to: receive a sequence of battery voltage samples from the voltage
sensor and a sequence of battery current samples from the current
sensor; determine a change in the battery voltage samples over a
predetermined number of samples and a change in the battery current
samples over the predetermined number of samples; check whether a
ratio of the change in the battery voltage samples and the change
in the battery current samples is within an expected range for one
of (i) a resistance of the battery and (ii) a conductance of the
battery; and detect the fault in the current sensor based on
whether the ratio is within the expected range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The foregoing aspects and other features of the system and
method for detecting a sensor fault in a battery system are
explained in the following description, taken in connection with
the accompanying drawings.
[0006] FIG. 1 shows a battery system according to the
disclosure.
[0007] FIG. 2 shows a method of detecting a current sensor fault in
a battery system.
[0008] FIG. 3 shows exemplary sequences of battery voltage samples
and battery current samples.
DETAILED DESCRIPTION
[0009] For the purposes of promoting an understanding of the
principles of the disclosure, reference will now be made to the
embodiments illustrated in the drawings and described in the
following written specification. It is understood that no
limitation to the scope of the disclosure is thereby intended. It
is further understood that the present disclosure includes any
alterations and modifications to the illustrated embodiments and
includes further applications of the principles of the disclosure
as would normally occur to one skilled in the art which this
disclosure pertains.
[0010] FIG. 1 shows a battery system 100 according to the
disclosure. In at least one embodiment, the battery system 100 is
integrated into a vehicle, such as an electric vehicle or a
full/mild/micro hybrid-electric vehicle. The battery system 100
includes a battery 102 operably connected and configured to provide
power to loads 104. In at least one embodiment, the battery 102
comprises a plurality of individual battery cells 106 connected in
series and/or in parallel with one another to provide an output
voltage of the battery 102 (e.g. 12 Volts, 48 Volts, 200+ Volts)
between a positive battery terminal 108 and a negative battery
terminal 110. The battery cells 106 may comprise any of various
types of battery cells, such as nickel-metal hydride or
lithium-ion.
[0011] The loads 104 are connected to the battery 102 and
configured to receive power from the battery 102 during operation.
In some embodiments, the loads 104 are connected to the positive
battery terminal 108 via a high-side switch 112 and to the negative
battery terminal 110 via a low-side switch 114. The switches 112
and 114 may comprise electromechanical switches, such a relays or
contactors, or electronic switches, such as power
metal-oxide-semiconductor field-effect transistors (power MOSFET)
or insulated-gate bipolar transistors (IGBT). In some embodiments,
the loads 104 may include a traction motor of the vehicle or a
vehicle electrical system. In some embodiments, the battery system
100 may include various power electronics (not shown) connected
between the battery 102 and some or all of the loads 104, such a
DC/DC converter configured to step down the battery voltage to that
of the vehicle electrical system.
[0012] The battery system 100 further includes a current sensor
116, a voltage sensor 118, and a temperature sensor 120. The
current sensor 116 is configured to measure a battery current I
that flows through the battery 102. In one embodiment, the current
sensor 116 includes a shunt resistor arranged in series with the
battery 102 which provides a voltage that is proportional to the
battery current I. In one embodiment, the current sensor 116
comprises a Hall Effect sensor arranged in series with the battery
102 and configured to measure the battery current I. The voltage
sensor 118 is connected in parallel with the battery 102 and is
configured to measure a battery voltage U across the positive and
negative battery terminals 108 and 110 of the battery 102. In some
embodiments, the voltage sensor 118 is further configured to
measure voltages of individual cells 106 of the battery 102. The
temperature sensor 120 is configured to measure a battery
temperature T of the battery 102. In one embodiment, the
temperature sensor 120 comprises several individual temperature
sensors and the measured battery temperature T may be an minimum,
maximum, or average of several measurements from the different
sensors.
[0013] The battery system 100 further includes a controller 122,
which is operably connected to the current sensor 116, the voltage
sensor 118, and the temperature sensor 120. The controller 122 is
configured to receive measurement values of the battery voltage U
and the battery current I from the current sensor 116 and the
voltage sensor 118. The controller 122 is at least configured to
detect sensor faults of the current sensor 116. The controller 122
generally comprises at least one processor and at least one
associated memory having program instructions stored thereon, which
are executed by the at least one processor to achieve the described
functionalities. It will be recognized by those of ordinary skill
in the art that a "controller" or "processor" includes any hardware
system, hardware mechanism or hardware component that processes
data, signals, or other information. The controller 122 may include
a system with a central processing unit, multiple processing units,
or dedicated circuitry for achieving specific functionality. In
some embodiments, the controller 122 is a battery management
system, or a component thereof, which is configured to serve other
functions in addition to sensor fault detection. In some
embodiments, the controller 122 is operably connected to the
switches 112 and 114 and configured to command the switches 112 and
114 to open and close. In some embodiments, the controller 122 is
operably connected to an output device 124 and configured to
operate the output device 124 to generate audible or visual alert.
The output device 124 may comprise a speaker, a light, a display
screen, or the like.
[0014] Various methods for detecting a sensor fault in the battery
system are described below. In the description of the methods,
statements that the method is performing some task or function
refers to a controller or general purpose processor executing
programmed instructions stored in non-transitory computer readable
storage media operatively connected to the controller or processor
to manipulate data or to operate one or more components in the
system 100 to perform the task or function. Particularly, the
controller 122 above may be such a controller or processor and the
executed program instructions may be stored in a memory.
Additionally, the steps of the methods may be performed in any
feasible chronological order, regardless of the order shown in the
figures or the order in which the steps are described.
[0015] FIG. 2 shows a method 200 for detecting a sensor fault in a
battery system, such as the battery system 100. The method 200,
referred to herein as a "Paired Sample Correlation" method,
assesses a level of correlation between two sensor signals whose
relationship is approximately linear within small regions by
comparing of their relative behavior (i.e. relative change of the
signals over time, as opposed to relative magnitude). In this way,
the method is most useful for detecting a gain fault in the one of
the sensors. Additionally, the method 200 is described herein as
applied to a battery system having a single current sensor and a
voltage sensor and for the purpose of detecting a gain fault in a
current sensor. However, the method can be similarly applied to
other applications having sensors which measure correlated
signals.
[0016] The method 200 begins with a step of receiving a sequence of
battery voltage samples and a sequence of battery current samples
(block 210). Particularly, with respect to the embodiments
described in detail herein, the current sensor 116 is configured to
generate a sequence of measurement samples regarding a battery
current I which flows through the battery 102. Similarly, the
voltage sensor 118 is configured to generate a sequence of
measurement samples regarding a battery voltage U across the
battery terminals 108 and 110 of the battery 102. The controller
122 is configured receive the sequence of battery current samples
from the current sensor 116 and the sequence of battery voltage
samples from the voltage sensor 118. In some embodiments, the
current sensor 116 and the voltage sensor 118 may instead be
configured to generate analog measurement signals which are sampled
by the controller 122 to provide the sequence of battery current
samples and the sequence of battery voltage samples.
[0017] FIG. 3 shows exemplary sequences of battery voltage and
battery current samples. Particularly, the plot 302 shows a
sequence of battery voltage samples 304 generated by the voltage
sensor 118 and received by the controller 122. Similarly, the plot
306 shows a sequence of battery current samples 308 generated by
the current sensor 116 and received by the controller 122. As
shown, the battery voltage samples 304 and battery current samples
308 span a plurality of time steps from t=0 to t=18. In at least
one embodiment, the particular duration of time between each time
step is a function of the sampling rate of the current sensor 116
and the voltage sensor 118. In some embodiments, the current sensor
116 and the voltage sensor 118 are configured with a common
sampling rate and the time steps coincide with the common sample
period of the current sensor 116 and the voltage sensor 118. In
other embodiments, one of the sensors 116 and 118 has a sampling
rate which is an multiple of the other of the sensors 116 and 118
and the time step may coincide with the longer of the sampling
periods of the sensors 116 and 118, or otherwise coincide with a
common multiple of the sampling periods, such as the least common
multiple.
[0018] Returning to FIG. 2, the method 200 continues with a step of
determining a change in the battery voltage samples and a change in
the battery current samples (block 220). Particularly, with respect
to the embodiments described in detail herein, the controller 122
is configured to determine a change in the battery voltage .DELTA.U
over a predetermined number of samples and a change in the battery
current .DELTA.I over the predetermined number of samples.
Particularly, in at least one embodiment, the controller 122 is
configured to calculate the change in the battery voltage .DELTA.U
based on the expression .DELTA.U=U.sub.s-U.sub.s-w, where s is the
index for the current time step and w is the predetermined width of
the sampling window, which is a positive integer of one or greater.
Similarly, in at least one embodiment, the controller 122 is
configured to calculate the change in the battery current .DELTA.I
based on the expression .DELTA.I=I.sub.s-d-I.sub.s-w-d, where d is
a delay of the current relative to the voltage to compensate for
any phase difference between the battery current I and the battery
voltage U, which is a positive or negative integer or zero. For
example, d =1 will correlate the voltage sample U.sub.s with the
previous current sample I.sub.s-1 and d=-2 will correlate the
voltage sample U.sub.s with a subsequent current sample I.sub.s+2.
The phase difference between the battery current I and the battery
voltage U may be a result of small differences in latency between
the current sensor 116 and the voltage sensor 118, as well as any
reactances in the battery circuit. FIG. 3 illustrates an exemplary
battery voltage window 310 and battery current window 312, where
the current time step s=t=10 and the window width w=2.
Additionally, as shown, d=-3 in order to compensate for a delay of
the battery current I by three time steps relative to the battery
voltage U.
[0019] The method 200 continues with a step of checking whether a
ratio of the change in the battery voltage samples and the change
in the battery current samples is within an expected range for one
of (i) a resistance of the battery and (ii) a conductance of the
battery (block 230). Particularly, with respect to the embodiments
described in detail herein, the controller 122 is configured to
calculate a ratio of the change in the battery voltage .DELTA.U and
the change in the battery current .DELTA.I. In at least one
embodiment, the controller 122 is configured to calculate the ratio
according to the expression
.DELTA. U .DELTA. I = U s - U s - w I s - d - I s - w - d ,
##EQU00001##
but also may calculate the inverse ratio according to the
expression
.DELTA. I .DELTA. U = I s - d - I s - w - d U s - U s - w .
##EQU00002##
[0020] The controller 122 is configured to compare the ratio with
an estimated resistance R of the battery 102 in the case that the
ratio
.DELTA. U .DELTA. I ##EQU00003##
is formed, or an estimated conductance
1 R ##EQU00004##
of the battery 102 in the case that the ratio
.DELTA. U .DELTA. I ##EQU00005##
is formed. In some embodiments, the controller 122 is configured to
receive a temperature measurement T from temperature sensor 120,
and determine an estimated resistance R of the battery 102 based on
the measured temperature T using a mathematical model of the
battery 102 or a resistance vs. temperature look-up table stored in
an associated memory.
[0021] If the ratio is not sufficiently similar to the estimated
resistance or conductance of the battery 102, a fault in one of the
sensors 116 and 118 can be suspected. Particularly, the relative
behavior of the battery current and the battery voltage is largely
governed by Ohm's Law. Accordingly, when the sensors 116 and 118
are functioning appropriately, the ratio is expected to correspond
to the internal resistance or the internal conductance of the
battery 102. In some embodiments, the controller 122 is configured
to determine whether the ratio
.DELTA. U .DELTA. I ##EQU00006##
is within a predetermined range of the estimated resistance R or,
alternatively, whether the ratio
.DELTA. I .DELTA. U ##EQU00007##
is within a predetermined range of the estimated conductance
1 R . ##EQU00008##
Particularly, in one embodiment the controller 122 is configured to
determine whether the ratio is within an estimated range for the
resistance R according to the expression
R ( 1 + .delta. n ) < U s - U s - w I s - d - I s - w - d < R
( 1 + .delta. p ) , ##EQU00009##
where .delta..sub.n is the error in the estimated resistance R in
the negative direction (e.g. -50%) and where .delta..sub.p is the
error in the estimated resistance R in the positive direction (e.g.
59%). Alternatively, in the case that the ratio
.DELTA. I .DELTA. U ##EQU00010##
is formed, the controller 122 is configured to determine whether
the ratio is within an estimated range for the conductance
1 R ##EQU00011##
according to the expression
1 R ( 1 + .delta. n ) > I s - d - I s - w - d U s - U s - w >
1 R ( 1 + .delta. p ) . ##EQU00012##
In one embodiment, the controller 122 is configured to periodically
adjust over time the error .delta..sub.n and/or the error
.delta..sub.p as a function of the measured temperature T, a
performance of the temperature sensor 120, cell aging of the
battery 102, a pulse profile, the state of charge of the battery
102, a polarity of the battery current I, and/or an uncompensated
phase difference between the battery voltage U and the battery
current I. Additionally, in some embodiments, the controller 122 is
configured to adjust the error .delta..sub.n and/or the error
.delta..sub.p as a function manufacturing variability of the
battery 102, as a constant or one-time adjustment.
[0022] In some embodiments, the controller 122 is configured to
detect a fault in one of the current sensor 116 and the voltage
sensor 118 in response to the ratio being outside the estimated
range for the resistance R or the conductance
1 R . ##EQU00013##
In at least one embodiment, faults in the voltage sensor 118 are
detected using other detection processes, and the controller 122 is
configured to detect a fault of the current sensor 116 in response
to the ratio being outside the estimated range for the resistance R
or the conductance
1 R . ##EQU00014##
In such embodiments, the controller 122 may be further configured
to perform some kind of ameliorative operation in response to
detecting the sensor fault. In one embodiment, the controller 122
is configured to operate the switches 112 and 114 to open in
response to the detecting the fault, thereby disconnecting the
terminals 108 and 110 of the battery 102 from the loads 104. In one
embodiment, the controller 122 is configured to operate the output
device 124 to generate audible or visual alert in response to the
detecting the fault, thereby alerting a user of the detected sensor
fault. In one embodiment, the controller 122 is configured to
transmit a signal indicating the detected sensor fault to a higher
level controller for further processing, such as
On-Board-Diagnostics (OBD) evaluations using an in use monitoring
performance ratio (IUMPR) or other real time monitoring techniques.
In one embodiment, the controller 122 is configured to perform the
On-Board-Diagnostics (OBD) evaluations itself based on the
detection of the sensor fault.
[0023] However, in many embodiments, the method 200 instead
continues with a step of storing whether the ratio is outside the
expected range of the one of (i) the resistance of the battery and
(ii) the conductance of the battery (block 240). Particularly, with
respect to the embodiments described in detail herein, the
controller 122 is configured to store whether the ratio is outside
the estimated range for the resistance R or the conductance
1 R . ##EQU00015##
In one embodiment, the controller 122 is configured to increment a
counter (or omit a step of incrementing a counter) in response to
the ratio being outside the estimated range for the resistance R or
the conductance
1 R . ##EQU00016##
In this way, the controller 122 is configured to count a number of
times the check fails and/or passes. In one embodiment, the
controller 122 is configured to store the result of the comparison
(e.g. pass or fail, inside or outside) in association with the
respective time step.
[0024] The method 200 continues by repeating the steps of
determining the change in the battery voltage samples and the
change in the battery current samples (block 220), checking whether
the ratio of the change in the battery voltage samples and the
change in the battery current samples is within the expected range
for the one of (i) the resistance of the battery and (ii) the
conductance of the battery (block 230), and storing whether the
ratio is outside the expected range of the one of (i) the
resistance of the battery and (ii) the conductance of the battery
(block 240) for successive times steps of the battery voltage and
battery current samples. Particularly, for a plurality of
successive repetitions, the controller 122 is configured to
increment the time step s by at least one time step and compare a
ratio of the change in battery voltage and the change in battery
current with a known resistance or conductance. Particularly, in at
least one embodiment, for a plurality of successive repetitions,
the controller 122 is configured to increment the time step s by
one and reevaluate the expression
R ( 1 + .delta. n ) < U s - U s - w I s - d - I s - w - d < R
( 1 + .delta. p ) ##EQU00017##
or its inverse as discussed above. After each repetition, the
controller 122 is configured to increment a counter based on the
result or otherwise store the result in association with the
respective time step.
[0025] After a predetermined number of repetitions, the method 200
continues with a step of determining a number of times during the
predetermined number of repetitions that the ratio was outside the
expected range (block 250). Particularly, after a predetermined
number of successive repetitions, the controller 122 is configured
to determine a number of times during the predetermined number of
successive repetitions that the ratio was outside the estimated
range for the resistance R or the conductance
1 R . ##EQU00018##
In embodiments in which a counter was incremented in response to
each time the ratio was outside the estimated range for the
resistance R or the conductance
1 R , ##EQU00019##
the controller 122 is configured to read a value from the counter
to determine the number of times. In other embodiments, the
controller 122 is configured to read from memory the results
associated with the previous time steps of the predetermined number
of successive repetitions and count a number of times that the
ratio was outside the estimated range for the resistance R or the
conductance
1 R . ##EQU00020##
[0026] If the determined number of times exceeds a predetermined
threshold, the method 200 continues with a step of detecting a
fault in the current sensor in response thereto (block 260).
Particularly, the controller 122 is configured to detect a fault in
one of the current sensor 116 and the voltage sensor 118 in
response to the determined number of times that the ratio was
outside the estimated range for the resistance R or the
conductance
1 R ##EQU00021##
exceeding a predetermined threshold (e.g. 20%). In at least one
embodiment, faults in the voltage sensor 118 are detecting using
other detection processes, and the controller 122 is configured to
detect a fault of the current sensor 116 in response to the
determined number of times exceeding the predetermined threshold
(e.g. 20%). In one embodiment, the controller 122 is configured to
periodically adjust over time the predetermined threshold as a
function of the measured temperature T, a performance of the
temperature sensor 120, cell aging of the battery 102, a pulse
profile, the state of charge of the battery 102, a polarity of the
battery current I, and/or an uncompensated phase difference between
the battery voltage U and the battery current I. Additionally, in
some embodiments, the controller 122 is configured to adjust the
predetermined threshold as a function manufacturing variability of
the battery 102, as a constant or one-time adjustment.
[0027] In some embodiments, in response to detecting the sensor
fault, the controller 122 may be further configured to perform some
kind of ameliorative operation. In one embodiment, the controller
122 is configured to operate the switches 112 and 114 to open in
response to the detecting the fault, thereby disconnecting the
terminals 108 and 110 of the battery 102 from the loads 104. In one
embodiment, the controller 122 is configured to operate the output
device 124 to generate audible or visual alert in response to the
detecting the fault, thereby alerting a user of the detected sensor
fault. In one embodiment, the controller 122 is configured to
transmit a signal indicating the detected sensor fault to a higher
level controller for further processing, such as
On-Board-Diagnostics (OBD) evaluations using an in use monitoring
performance ratio (IUMPR) or other real time monitoring techniques.
In one embodiment, the controller 122 is configured to perform the
On-Board-Diagnostics (OBD) evaluations itself based on the
detection of the sensor fault.
[0028] After detecting or not detecting a fault in the current
sensor, the method 200 returns to the process of repeating the
steps of determining the change in the battery voltage samples and
the change in the battery current samples (block 220), checking
whether the ratio of the change in the battery voltage samples and
the change in the battery current samples is within the expected
range for the one of (i) the resistance of the battery and (ii) the
conductance of the battery (block 230), and storing whether the
ratio is outside the expected range of the one of (i) the
resistance of the battery and (ii) the conductance of the battery
(block 240) for successive times steps of the battery voltage and
battery current samples, until another predetermined number of
repetitions have been performed.
[0029] In some embodiments, the method 200 further includes a step
of determining whether the following boundary conditions are
satisfied: (1) the battery temperature exceeds a minimum
temperature threshold, (2) the change in the battery voltage
samples exceeds a minimum voltage change threshold, and/or (3) the
current value of the battery current samples exceeds a minimum
current threshold (block 270). Particularly, before checking
whether the ratio is outside the estimated range for the resistance
R or the conductance
1 R , ##EQU00022##
the controller 122 is configured to determine whether certain
boundary conditions are satisfied. If the boundary conditions are
not satisfied, the controller 122 is configured skip the step of
checking whether the ratio outside the estimated range for the
resistance R or the conductance
1 R ##EQU00023##
and simply move on to the next time step of the process. In one
embodiment, a boundary condition is that the current battery
temperature T is greater than a minimum temperature threshold
T.sub.min, or in other words, the expression T>T.sub.min must be
satisfied to avoid error due to large changes in cell internal
resistance at low temperatures. In one embodiment, a boundary
condition is that the change in the battery voltage .DELTA.U is
greater than a minimum change in battery voltage threshold
.DELTA.U.sub.min, or in other words, the expression
.DELTA.U>.DELTA.U.sub.min must be satisfied to avoid checks with
minimal changes in battery voltage. In one embodiment, a boundary
condition is that the current battery current I.sub.s is greater
than a minimum battery current threshold I.sub.min, or in other
words, the expression I.sub.s>I.sub.min must be satisfied to
avoid checks at low currents if necessary. In one embodiment, the
controller 122 is configured to determine whether each of the
boundary conditions T>T.sub.min, .DELTA.U>.DELTA.U.sub.min,
and I.sub.s>I.sub.min are satisfied and only check whether the
ratio is outside the estimated range for the resistance R or the
conductance
1 R ##EQU00024##
in response to all of the boundary conditions being satisfied. In
one embodiment, the controller 122 is configured to periodically
adjust over time the minimum temperature threshold T.sub.min, the
minimum change in battery voltage threshold .DELTA.U.sub.min,
and/or minimum battery current threshold I.sub.min as a function of
the measured temperature T, a performance of the temperature sensor
120, cell aging of the battery 102, a pulse profile, the state of
charge of the battery 102, a polarity of the battery current I,
and/or an uncompensated phase difference between the battery
voltage U and the battery current I. Additionally, in some
embodiments, the controller 122 is configured to adjust the minimum
temperature threshold T.sub.min, the minimum change in battery
voltage threshold .DELTA.U.sub.min, and/or minimum battery current
threshold I.sub.min as a function manufacturing variability of the
battery 102, as a constant or one-time adjustment.
[0030] The herein described paired sample correlation method
improves the functioning of the battery system 100 by enabling the
controller 122 to detect faults in the current sensor 116 without
the necessary inclusion of a secondary current sensor. Furthermore,
in battery systems which do include a secondary current sensor, the
paired sample correlation method enables the controller 122 to
provide further redundancy by detecting faults, particularly gain
faults, in the current sensor 116. Unlike some other methods, the
paired sample correlation method disclosed herein requires only a
small amount of data to begin producing results (e.g. two samples),
which is advantageous for real-time applications such as fault
detection in a battery system. Furthermore, the low computational
costs of each correlation check enable the method to run
continuously on low-performance and low-cost hardware. The paired
sample correlation method is easily calibrated due to intuitive
nature of calibration variables (e.g., the predetermined pass/fail
threshold or the values for the parameters .delta..sub.n,
.delta..sub.p, T.sub.min, .DELTA.U.sub.min, and/or I.sub.min as
discussed above) and low interdependence between calibration
variables. The paired sample correlation method advantageously has
logic which is more easily implemented because each type of
calculation is performed either for every new sample (for which the
boundary conditions are met) or every time the high-level
evaluation is performed. This is in contrast to algorithms where
some calculations are performed or not performed depending on the
result of other calculations.
[0031] While the disclosure has been illustrated and described in
detail in the drawings and foregoing description, the same should
be considered as illustrative and not restrictive in character. It
is understood that only the preferred embodiments have been
presented and that all changes, modifications and further
applications that come within the spirit of the disclosure are
desired to be protected.
* * * * *